In order to understand the mechanism of cell transformation and virus replication in Rous sarcoma virus (RSV) infected cells, various approaches will be made. Characterization of newly obtained sarcoma viruses recovered from chicken or quail tumors induced by transformation defective mutants of RSV will be continued. This will include their genome RNA as well as their src gene product. Comparison of src gene will be extended to various strains to see the degree of homology. An attempt will be made to determine the exact location of deletion in td mutants in order to understand the process of recombination leading the generation of sarcoma virus. Recently, we found that Fujinami sarcoma virus does not contain src gene which is present in all other avian sarcoma virus. The transforming gene and its product of Fujinami virus will be examined.